He missed his chance to say thank you and goodbye to viewers as the technical glitch lasted so long that it forced the channel to head straight to 7.30.

Ian Henderson's final ABC bulletin went down during a story about Bill Shorten on Thursday.Credit:AAP

Some viewers took to Twitter to vent their confusion and disappointment.

ABC Melbourne later tweeted an apology, saying Henderson was amused by the glitch and would say goodbye Friday night.

An ABC spokesman said an "unexpected technical fault" was to blame for the switch to a back-up transmission from NSW.

"The timing of this fault during Ian Henderson’s scheduled final bulletin was unfortunate, to say the least," he said in a statement.

"The good news is that Hendo will now be back on air at 7pm tomorrow to present his final, final ABC News Victoria bulletin."

The spokesman said the cause of the fault was being investigated and reiterated the station's earlier apology.

The broadcaster's acting news director, Craig McMurtrie, said there was no way they would let Henderson go without a proper goodbye and invited viewers to tune in again on Friday night for the farewell "he so richly deserves".

“I’m embarrassed by what happened but Hendo is such a gentleman that the way he took it in his stride is humbling," he said.